The present invention relates to circuit board construction. More specifically, the present invention relates to an apparatus and method for performing a function, such as burning-in, testing or programming on an integrated circuit.
For years, it has been customary to employ printed circuit boards or printed circuit assemblies as media for mechanically holding electronic components and providing operative electrical connections between the components. Typically, printed circuit boards or printed circuit assemblies comprise an insulating substrate or layer upon which a layer of conductive metal was deposited or bonded. The metal coating layer was etched by a chemical process to form a predetermined pattern of conductive traces on the surfaces of the substrate. Alternatively, the conductive traces were deposited onto the insulator using selective deposit techniques, such as masks. These electrical conductive traces could be formed on both sides of the substrate to allow conductors to cross without coming in contact with one another. A plurality of vias or plated through holes were formed through the metal layers and the insulating substrate and were positioned to receive leads from the electronic components.
As circuit board technology developed, designers began to create circuit boards comprising many alternating insulating substrate and conductive layer pairs, resulting in sandwiched circuit boards that could accommodate a higher component density. In addition, surface mount technology allowed the leads to be soldered to solder pads on the surface of the circuit board, rather than requiring the leads to pass through and be soldered to through holes.
Electronic components themselves also underwent changes to accommodate higher density. First, integrated circuits were originally placed in dual in-line packages, each consisting of an elongated plastic or ceramic body encapsulating the integrated circuit and a plurality of electrical leads coupled to the integrated circuit and arranged in a series extending from the two long edges of the body. The leads could either be through hole soldered or surface mounted. However, the number of leads that a dual in-line package could accommodate was a function of the length of the dual in-line package body edges. Later, packages were provided having leads extending from all four edges of the body. However, the number of leads was still a function of the perimeter of the body edges.
In a further effort to increase lead density, designers developed quad-flat packs comprising generally square bodies having leads extending downward from the lower surface of the body. The leads were typically arranged in multi rows and columns, allowing the quad-flat packs to accommodate more pins than dual in-line packages. However, limitations in socket size and collective lead insertion force began to be problematic.
Presently, designers are focusing on ball grid array packaging wherein leads are replaced with a finely pitched matrix of conductive contact surfaces on the lower surface of an otherwise conventional body. The circuit board to which a ball grid array package is to be mounted is conventionally provided with a matrix of corresponding surface mounted flat pad structures upon each of which is deposited a small quantity of solder. To mount the ball grid array package to the circuit board, the ball grid array package is temporarily clamped to the board and the board is heated, causing the solder to melt fusing the corresponding surfaces together and yielding a strong mechanical and electrical connection when cooled.
Ball grid array packaging provides a powerful tool in the further miniaturization of computers. However, systems designed to burn-in, test or program the components are lagging in technology. Thus, there is a continuing need for a system which is capable of testing, burning-in, or programming an integrated circuit.